U.S. patent number 7,897,201 [Application Number 11/703,830] was granted by the patent office on 2011-03-01 for method for manufacturing magnetoresistance effect element.
This patent grant is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Yoshihiko Fuji, Hideaki Fukuzawa, Hitoshi Iwasaki, Hiromi Yuasa.
United States Patent |
7,897,201 |
Yuasa , et al. |
March 1, 2011 |
**Please see images for:
( Certificate of Correction ) ** |
Method for manufacturing magnetoresistance effect element
Abstract
A method is for manufacturing a magnetoresistance effect element
having a magnetization fixed layer, a non-magnetic intermediate
layer, and a magnetization free layer being sequentially stacked.
The method includes: forming at least a part of a magnetic layer
that is to become either one of the magnetization fixed layer and
the magnetization free layer; forming a function layer including at
least one of an oxide, a nitride, and a fluoride on the part of the
magnetic layer; and removing a part of the function layer by
exposing the function layer to either one of an ion beam and plasma
irradiation.
Inventors: |
Yuasa; Hiromi (Kawasaki,
JP), Fukuzawa; Hideaki (Kawasaki, JP),
Fuji; Yoshihiko (Kawasaki, JP), Iwasaki; Hitoshi
(Yokosuka, JP) |
Assignee: |
Kabushiki Kaisha Toshiba
(Tokyo, JP)
|
Family
ID: |
38444324 |
Appl.
No.: |
11/703,830 |
Filed: |
February 8, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070202249 A1 |
Aug 30, 2007 |
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Foreign Application Priority Data
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Feb 9, 2006 [JP] |
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P2006-032261 |
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Current U.S.
Class: |
427/131; 427/127;
216/66; 427/535; 216/63; 427/130; 427/551; 427/532; 427/576;
427/132; 216/76; 216/67 |
Current CPC
Class: |
H01F
10/3272 (20130101); B82Y 10/00 (20130101); B82Y
25/00 (20130101); G11B 5/3909 (20130101); B82Y
40/00 (20130101); G01R 33/093 (20130101); H01F
41/303 (20130101); G11B 5/3929 (20130101); H01F
10/3281 (20130101); G11B 5/3163 (20130101); G11B
2005/3996 (20130101); H01F 10/3259 (20130101); H01F
41/325 (20130101) |
Current International
Class: |
G11B
21/00 (20060101); B05D 3/00 (20060101); H05H
1/00 (20060101); C23F 3/00 (20060101) |
Field of
Search: |
;427/130-131,532,551,535
;216/76 |
References Cited
[Referenced By]
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Primary Examiner: Meeks; Timothy H
Assistant Examiner: Louie; Mandy C
Attorney, Agent or Firm: Nixon & Vanderhye, PC
Claims
What is claimed is:
1. A method for manufacturing a magnetoresistance effect element
having a magnetization fixed layer, a non-magnetic intermediate
layer, and a magnetization free layer which are sequentially
stacked, the method comprising: forming at least a part of either
one of the magnetization fixed layer and the magnetization free
layer; forming a further layer including at least one of an oxide,
a nitride, and a fluoride on the part of the one of the
magnetization fixed layer and the magnetization free layer; and
exposing the further layer to either one of an ion beam and plasma
irradiation to uniformly reduce a thickness of the further layer
and provide a function layer of uniform thickness on the part of
the one of magnetization fixed layer and the magnetization free
layer.
2. The method according to claim 1, wherein the ion beam is
irradiated at a voltage of 110V or less.
3. The method according to claim 1, wherein the plasma irradiation
is performed at a plasma power in a range from 15W to 30W.
4. The method according to claim 1, further comprising forming the
non-magnetic intermediate layer by a conductive material.
5. The method according to claim 1, further comprising forming the
non-magnetic intermediate layer by a non-conductive material.
6. A method for manufacturing a magnetoresistance effect element
having a magnetization fixed layer, a non-magnetic insulating
intermediate layer, and a magnetization free layer which are
sequentially stacked, the method comprising: forming the
non-magnetic insulating intermediate layer by one of an oxide, a
nitride, and a fluoride; and exposing the non-magnetic insulating
intermediate layer to either one of an ion beam and plasma
irradiation to uniformly reduce a thickness of the non-magnetic
insulating intermediate layer to provide a non-magnetic insulating
intermediate layer of uniform thickness.
Description
RELATED APPLICATION(S)
The present disclosure relates to the subject matter contained in
Japanese Patent Application No. 2006-032261 filed on Feb. 9, 2006,
which is incorporated herein by reference in its entirety.
FIELD
The present invention relates to a method for manufacturing a
magnetoresistance effect element having a structure of causing a
flow of a sense current in a direction perpendicular to a film
plane of a magnetoresistance effect film, as well as to a
magnetoresistance effect element, a magnetoresistance effect head,
a magnetic recording-and-reproducing apparatus, and a magnetic
storage device.
BACKGROUND
There has hitherto been reported an example where, even when a
ferromagnetic layer is not subjected to anti-ferromagnetic coupling
in relation to Current-In-Plane (CIP)-Giant-Magnetoresistance (GMR)
that is acquired by causing an electric current to flow through the
surface of a multilayer film of a sandwich structure of [a
ferromagnetic layer/a non-magnetic layer/a ferromagnetic layer], a
great magnetoresistance effect appears. Specifically, an
alternating bias magnetic field is applied to one of two
ferromagnetic layers with a nonmagnetic layer being sandwiched
therebetween, to thus fix magnetization (the layer is called a
"magnetization fixed layer" or a "pin layer"). The other
ferromagnetic layer is reversely magnetized (called a
"magnetization free layer" or a "free layer") by an external
magnetic field (a signal magnetic field or the like). Thus, a
relative angle between magnetizing directions of the two
ferromagnetic layers arranged with a non-magnetic layer sandwiched
therebetween is changed, whereby a great magnetic resistance effect
is achieved. A multilayer of such a type is called a "spin valve".
See the following related-art document 1 for detail.
Related-art document 1: "Phys. Rev. B45, 806(1992), J. Appl. Phys.
69, 4774 (1981)"
Since the spin valve can saturate magnetization at low magnetic
field strength, the spin valve is suitable for use as an MR head.
Although an MR head has already been put into practice, under
present circumstances the rate of change in magnetic resistance of
the MR head remains a maximum of about 20%. An MR element
exhibiting a higher rate of change in magnetic resistance
(hereinafter referred to as an "MR ratio") has been required.
A TMR (Tunneling MagnetoResistance) element utilizing a tunnel
effect is mentioned as a candidate for such an MR element. However,
such an effect is exhibited as a result of electrons tunneling
through an insulation layer. Hence, the TMR element usually has
high resistance. When the MR head has high resistance, there arises
a problem of a magnetic head incorporated in a hard disk drive
generating large noise. In order to reduce the resistance, the
thickness of a barrier layer must be reduced. However, it is known
that, when the barrier layer is made thin, a uniform MR head cannot
be manufactured, so that the MR ratio is deteriorated by pin holes.
In relation to the TMR element, difficulty is encountered in
achieving compatibility between low resistance and a high MR ratio.
In the TMR, an electric current is caused to flow in a direction
perpendicular to the film plane, and hence recording density of the
hard disk is increased. When the size of the TAR head is reduced,
resistance is increased further, which makes the head difficult to
use.
In contrast, a CPP (Current-Perpendicular-to-Plane)--GMR element is
mentioned as a candidate, wherein a sense current is caused to flow
in a direction perpendicular to the film plane of an element. In
the GMR element, electrons conduct through metal to thus appear.
Hence, the GMR element has an advantage of low resistance. However,
in the case of the spin spine valve film, the resistance to
vertical conduction of an electric current is small. Hence, it is
considerably important to increase the resistance value of an area
in the film that contributes to spin-dependent conduction, thereby
increasing the amount of change in resistance.
In order to increase the amount of change in resistance; namely, to
improve the magnetoresistance effect, there has been conceived a
technique for inserting a resistance adjustment layer including an
insulator into a film of the spin valve. See the following
related-art document 2 for detail.
Related-art document 2: "J. Appl. Phys. 89, 6943 (2001), IEEE
Trans. Magn. 38, 2277 (2002)"
The spin valve is formed from an area that subjects electrons to
spin-dependent scattering (a magnetization fixed layer/a spacer
layer/a magnetization free layer) and an area where the degree of
spin-dependent scattering is low (a ground layer, an
anti-ferromagnetic layer, a protective layer, and the like).
Provided that the resistance of a former area is taken as Rsd and
the resistance of the latter area is taken as Rsi, the
magnetoresistance effect of the spin valve can be expressed as
.DELTA.Rsd/(Rsi+Rsd). As a result of attention being paid to an
phenomenon of enhancing the magnetoresistance effect of the
magnetoresistance effect becoming greater as Rsd is greater than
Rsi, a resistance adjustment layer including an insulator is
inserted as mentioned previously.
However, the enhancement of magnetoresistance effect solely
achieved solely by the current confinement effect is limited. In
order to further enhance the magnetoresistance effect, it is
necessary to increase spin-dependent scattering factors of the
magnetization fixed layer and those of the magnetization free
layer. To this end, studies on half metal become active. Here, an
expression "half metal" is generally defined as a magnetic material
having the status density of only either up-spin electrons or
down-spin electrons when the status of electrons in the vicinity of
a Fermi level is viewed. When idealistic half metal can be
materialized, there can be realized two statuses; namely, a state
where resistance is infinite and another state where resistance is
low, when the magnetization status of the magnetization fixed layer
and the magnetization status of the magnetization free layer are
anti-parallel to each other and when those are parallel to each
other. Therefore, an infinite rate of change in MR can be achieved.
In reality, even though thus far an idealistic state cannot be
materialized, when a difference between the state density of
up-spin electrons and the state density of down-spin electrons is
greater than that achieved in the related-art material, remarkable
and order-of-magnitude increases in the MR ratio are expected.
However, half metal encounters a great problem of hindering
commercialization. Specific problems are as follows. (1) In the
case of perovskite-based half metal, an improvement in
crystallinity is indispensable. However, in the case of a
polycrystalline film employed in a magnetic head, an improvement in
crystallinity is essentially impossible. (2) In general, a
temperature at which a half metal characteristic can be maintained
is low, and half metal hardly appears at room temperature. (3)
There is the possibility of a half metal characteristic
disappearing at an interface between different materials
constituting a spacer layer interposed between the magnetization
fixed layer and the magnetization free layer. Among them, problem
(3) is fatal. Even when perfect half metal can be manufactured at
room temperature, properties of half metal cannot be effectively
utilized when a TMR film or a CPP-GMR film is formed by stacking
half metal during formation of the spacer layer.
Incidentally, from the viewpoint of the magnetoresistance effect
element, perfect half metal is not required. The essential
requirement is an improvement in a ratio of spin polarization in
the electrons conducting through the sense current; specifically, a
ratio of spin polarization of electrons at Fermi level contributing
to conduction. Proposed technique is to pay attention to the spin
polarization ratio and to insert a function layer for modulating a
band structure into the magnetization fixed layer and the
magnetization free layer.
According to this technique, the function layer is formed from a
very thin oxidation layer and the like. This means is based on a
suggestion that, when an ultra-thin oxidation layer is inserted
into the magnetization fixed layer or the magnetization free layer
formed from metal, a spin is polarized in the vicinity of the
interface. When the oxidation layer becomes thick, the resistance
of an element is increased, and adverse effects, such as noise, are
imposed on the element as in the case of a related-art TMR element.
Accordingly, the oxidation layer is formed to a very-thin layer of
the order of one atom, to thus enable an attempt to reduce
resistance.
However, in general, when the function layer is formed to a
thickness of the order of one atom layer as shown in FIG. 11, the
function layer assumes the shape of an island, or a plurality of
pin holes are opened. Thus, difficulty is encountered forming a
uniform function layer. When holes are opened in the function
layer, an electric current induced by electrons having passed
through the holes turns into a shunt current, thereby ending in a
failure to attain great spin-dependent scattering. As a result, the
spin filtering effect is diminished. Accordingly, the function
layer must be very thin and uniform.
SUMMARY
According to a first aspect of the invention, there is provided a
method for manufacturing a magnetoresistance effect element having
a magnetization fixed layer, a non-magnetic intermediate layer, and
a magnetization free layer being sequentially stacked. The method
includes: forming at least a part of a magnetic layer that is to
become either one of the magnetization fixed layer and the
magnetization free layer; forming a function layer including at
least one of an oxide, a nitride, and a fluoride on the part of the
magnetic layer; and removing a part of the function layer by
exposing the function layer to either one of an ion beam and plasma
irradiation.
According to a second aspect of the invention, there is provided a
method for manufacturing a magnetoresistance effect element having
a magnetization fixed layer, a non-magnetic insulating intermediate
layer, and a magnetization free layer being sequentially stacked.
The method includes: forming the non-magnetic insulating
intermediate layer by one of an oxide, a nitride, and a fluoride;
and removing a part of the non-magnetic insulating intermediate
layer by exposing the non-magnetic insulating intermediate layer to
either one of an ion beam and plasma irradiation.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a structural drawing of a magnetoresistance effect
element according to first through eighth embodiments of the
present invention;
FIGS. 2A-2E are drawings pertaining to formation of a function
layer and a barrier layer of the present invention;
FIG. 3 is a view showing a spin filtering effect of the function
layer prepared through a process of the present invention;
FIG. 4 is a structural drawing of a magnetoresistance effect
element according to a first modification of the first embodiment
of the present invention;
FIG. 5 is a structural drawing of a magnetoresistance effect
element according to a second modification of the first embodiment
of the present invention;
FIGS. 6A and 6B shows a TEM image of the function layer prepared
through process of the present invention and a TEM image of a
function layer prepared through a related-art process,
respectively;
FIG. 7 is a graph showing a correlation between an applied voltage
and an MR ratio in AIT treatment during the process of the present
invention;
FIG. 8 is a structural drawing of a magnetoresistance effect
element according to a ninth embodiment of the present
invention;
FIG. 9 is a structural drawing of a magnetoresistance effect
element according to a seventh embodiment of the present
invention;
FIG. 10 is a structural drawing of a magnetoresistance effect
element according to a tenth embodiment of the present
invention;
FIG. 11 is a view showing a spin filtering effect of the function
layer prepared through a related-art process;
FIG. 12 is a table showing process requirements for samples made in
accordance with the embodiment;
FIG. 13 is a table showing process requirements for samples made in
accordance with the embodiment;
FIG. 14 is a table showing process requirements for samples made in
accordance with the embodiment;
FIG. 15 is a table showing process requirements for samples made in
accordance with the embodiment;
FIG. 16 is a table showing process requirements for samples made in
accordance with the embodiment;
FIG. 17 is a table showing results of measurement of the MR ratios
for the samples;
FIG. 18 is a table showing results of measurement of the MR ratios
for the samples;
FIG. 19 is a table showing results of measurement of the MR ratios
for the samples;
FIG. 20 is a table showing a comparison between the magnitude of
the MR ratio acquired in the samples of magnetoresistance effect
element; and
FIG. 21 is a table showing process requirements for samples made in
accordance with the embodiment.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Embodiments of the present invention will be described hereinbelow
by reference to the accompanying drawings.
First Embodiment
First, a magnetoresistance effect element manufactured by a
manufacturing method of a first embodiment of the present invention
will be described. FIG. 1 is a cross-sectional view of the
magnetoresistance effect element manufactured by the manufacturing
method of the present invention.
The magnetoresistance effect element shown in FIG. 1 has a
structure formed by stacking a first electrode 1; a substrate layer
2 formed from a Ta layer having a thickness of 5 nm and an Ru layer
having a thickness of 2 nm; an anti-ferromagnetic layer 3 formed
from PtMn to a thickness of 15 nm or thereabouts; a magnetization
fixed layer 4 including a first magnetization fixed layer 4-1
formed from a material of Co.sub.90Fe.sub.10 to a thickness of 3 to
4 nm or thereabouts, a magnetization anti-parallel bonding layer
4-2 formed from Ru to a thickness of about 0.9 nm, and a second
magnetization fixed layer 4-3 bonded to the Co.sub.90Fe.sub.10
layer of about 1.5 nm with a function layer 10-1 sandwiched
therebetween; a spacer layer 5 formed from Cu to a thickness of 3
nm or thereabouts; a magnetization free layer 6; a first protective
layer 7; a second protective layer 8; and a second electrode 9.
Magnetization of the first magnetization fixed layer 4-1 is fixed
essentially in one direction by an adjacent anti-ferromagnetic
layer 3. Magnetization of the second magnetization fixed layer 4-3
is fixed in a direction anti-parallel to the first magnetization
fixed layer via the magnetization anti-parallel coupling layer 4-2.
The magnetization free layer 6 includes a ferromagnetic layer whose
magnetization can change according to the external magnetic field.
The spacer layer 5 is a layer which blocks magnetic coupling
between the second magnetization fixed layer 4-3 and the
magnetization free layer 6. In the magnetoresistance effect element
shown in FIG. 1, the spacer layer 5 is formed from only metal.
The magnetoresistance effect element having the above configuration
is manufactured as mentioned above. First, a Ta layer of 5 nm and
an Ru layer of 2 nm are stacked on a material, such as Cu, NiFe,
Ta, Ru, CuAg, or the like, which is to become the first electrode
1, by DC magnetron sputtering, to thus form the substrate layer
2.
PtMn, which is to become the anti-ferromagnetic layer 3, is formed
on the substrate layer 2 to 15 nm, by DC magnetron sputtering
without breaking the atmosphere under which the substrate layer 2
has been formed. After formation of the anti-ferromagnetic layer 3,
Co.sub.90Fe.sub.10 is stacked to 3 to 4 nm on the
anti-ferromagnetic layer 3, thereby forming the first magnetization
fixed layer 4-1. As a result of Ru being stacked to 0.9 nm, the
magnetization anti-parallel coupling layer 4-2 is formed.
Subsequently, Co.sub.90Fe.sub.10--which is the stacked member;
i.e., the second magnetization fixed layer 4-3--is stacked to 1.5
nm. During the course of formation of the second magnetization
fixed layer 4-3, the function layer 10-1 is formed in the second
magnetization fixed layer 4-3 by such a process as shown in FIGS.
2A-2E.
Specifically, the process is as follows. First, Fe is grown to a
thickness of 1 nm as a portion of the second magnetization fixed
layer 4-3 that is to become an oxidized layer. Here, the term "a
portion of the second magnetization fixed layer 4-3" means a lower
half of the second magnetization fixed layer that is split into
upper and lower portions with the function layer 10 sandwiched
therebetween.
The surface of Fe, which is a portion of the second magnetization
fixed layer 4-3, is subjected to natural oxidation, ion beam
oxidation (IAO: Ion Assisted Oxidation), or plasma oxidation,
thereby causing a function layer 10-1 to grow to a thickness of
about 1.5 nm to 3 nm on the surface of Fe. Here, IAO is a process
for introducing oxygen into a chamber while exposing oxygen to an
Ar ion beam to thus effect oxidization. See the following
related-art document 3 for detail.
Related-art document 3: "J. Appl. Phys. 91, 6684 (2002)"
An ion beam is extremely weaker than that employed in ordinary
milling requirements, and a beam voltage is set to 100V or less. An
etch rate achieved when Fe is exposed to an ion beam without oxygen
under these requirements is 0.1 to 3 angstrom/min. or
thereabouts.
Process requirements for natural oxidization, IAO, and plasma
oxidization are as provided in Table 1 shown in FIG. 12.
In Table 1, reference symbol REF denotes, as a sample to be
referred to, a process for a spin valve structure having no
function layer. Reference symbols A-1 to A-4 denote process
conditions for a related-art process of preparing a function layer.
Reference symbols B-1 to B-4 denote process conditions for a
process of preparing a function layer of the present invention.
A difference between the process conditions for the conventional
process of preparing a function layer and the process conditions
for the process of the present invention for preparing a function
layer lies in that AIT (After Ion Treatment); namely, irradiation
of a weak ion beam, is performed when a thin oxide film is formed
by any one of natural oxidation, IAO, and plasma oxidation. AIT is
for forming a thin film from Fe.sub.50Co.sub.50--O by very weak
milling. As in the case of previously-described IAO, very weak ion
beam conditions are required in this case. For instance, when AIT
is performed under the conditions of a beam voltage of 200V or more
and a beam current of 100 mA or more, which are employed in a case
where a thick film of the order of tens of nanometers is removed by
milling, the uniform function layer 10 cannot be prepared as shown
in FIG. 11; otherwise, a treated film surface becomes rough, which
in turn reduces the MR ratio because the sense electron current 17
flows only partially through the function layer 10. AIT does not
result in the function layer being formed into the shape of an
island or a plurality of pin holes being formed in the function
layer. An oxide film to become the function layer 10 can be formed
into a thin film having a uniform thickness as shown in FIG. 3. In
Result, the whole of current 17 can flow through the function layer
10, so the high MR ratio can be obtained.
After the function layer 10 has been formed by the above process,
Co90Fe10 which is to form an upper half of the second magnetization
fixed layer 4-3 is formed, thereby completing the second
magnetization fixed layer 4-3. Next, the spacer layer 5 made from
Cu is formed over the second magnetization fixed layer 4-3 to a
thickness of 3 nm.
After formation of the spacer layer 5, the magnetization free layer
6 is formed. As in the case of the second magnetization fixed layer
4-3, the magnetization free layer 6 may include a function layer
10-2. A manufacturing process employed at this time is essentially
the same as the process for manufacturing the second magnetization
fixed layer 4-3, and hence its explanation is omitted.
After formation of the magnetization free layer 6, the first
protective layer 7 made from Cu and the second protective layer 8
made from Ru are formed, while continually remaining under vacuum,
by magnetron sputtering using a DC bias.
Finally, a material, such as Cu, NiFe, Ta, Ru, CuAg, or the like,
is caused to grow on the surface of the second protective layer 8,
thereby forming a second electrode 9. Through the above-mentioned
processes, the magnetoresistance effect element is completed.
In the present embodiment, the function layer 10 is taken as an
oxide of Fe. However, the function layer 10 is not limited to this
material. The essential requirement for the function layer 10 is to
be an oxide, a nitride, or a fluoride formed by oxidizing,
nitriding, or fluorinating metal or an alloy containing at least
one member selected from the group consisting of Fe, Co, Ni, Cu,
Ti, V, Cr, Mn, Mg, Al, Si, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W,
Re, Ir, Pt, and Au.
A difference between the properties of the magnetoresistance effect
element manufactured under the manufacturing method according to
the first embodiment of the present invention and those of the
magnetoresistance effect element manufactured under the
conventional manufacturing method will now be described by
reference to Table 1.
In Table 1, in A-1, A-2, A-3, and A-4, where the function layer 10
is formed through the related-art processes, an MR ratio is
increased as compared with a sample REF where the function layer is
not formed. However, a significant increase is not found. In
contrast, in B-1, B-2, B-3, and B-4 that are samples where the
function layer 10 is formed through the process of the present
invention, corresponding to samples prepared through the processes
of the present invention, the MR ratio is increased by a factor of
ten. Thus, the advantage of the samples is noticeable. The reason
for this is that a uniform function layer, such as that shown in
FIG. 3, is considered to be formed in the samples B-1, B-2, B-3,
and B-4, in contrast with the function layers of the samples A-1,
A-2, A-3, and A-4 being formed into the shape of an island as shown
in FIG. 11.
FIG. 6A shows a cross-sectional TEM (transmission electron
microscope) image of an area in the vicinity of the function layers
10-2, 10-2 prepared through the process of the present invention.
In the illustrated samples, the function layers 10-1, 10-2 are
oxide layers, and hence contrast which is whiter than that of the
surrounding areas is acquired. By the white contrast, a
determination can be made as to whether or not the function layers
are uniform or assume the shape of a fragmented island. As can be
ascertained in FIG. 6A, even when the sample is sliced as thinly as
possible in the direction of transmission of electrons, the
function layers 10-1, 10-2, which are essentially straight, have no
discontinuity, and are extremely thin. Meanwhile, FIG. 6B is a
cross-sectional TEM of an area of the function layers 10-1, 10-2
prepared through related-art processes. In contrast with FIG. 6A,
the function layers 10-1, 10-2 can be ascertained to have
discontinuity.
In FIGS. 6A and 6B, the function layers 10-1, 10-2 are white and
can be clearly distinguished from the other areas. When the
function layers are difficult to distinguish, the function layers
can also be identified by EDX (Energy Dispersive X-ray
Spectroscopy) analysis employing a beam whose size is narrowed to 1
nm or thereabouts. In this case, measurement points are provided at
intervals of 0.5 nm to 1 nm in the direction of growth of a film.
The function layers can also be computed from a half-value width of
the distribution of concentration of oxygen, nitride, phosphor,
fluorine, or the like achieved when the distribution of an element
is plotted with reference to the measurement positions.
FIG. 7 shows a result acquired when conditions for AIT have been
changed with respect to the sample B-2, which is a typical example
process of the present invention. A processing time was adjusted
and changed such that a film is formed to a thickness of 0.3 nm
from Fe.sub.50Co.sub.50--O. As can be seen from the result, when
the beam voltage has exceeded 110V, the MR ratio decreases. When
the beam voltage is increased to 210V, the MR ratio is understood
to assume a value of 0.3%, which is lower than the MR ratio
achieved in the case of the sample REF having no function layer.
From the result of this experiment, the beam voltage of AIT is
preferably 110V or less.
Irradiation of RF plasma also requires very weak energy conditions.
The energy is appropriately set to a range of 15 W to 30 W. In
contrast, under the strong condition of 100 W or the like used for
cleaning a substrate, the surface of the film is deteriorated, so
that the MR ratio is decreased.
First Modification
FIG. 4 shows a magnetoresistance effect element having a single
magnetization fixed layer rather than a three-layer structure (a
synthetic structure), as a first modification of the first
embodiment illustrated in FIG. 1.
In FIG. 4, the magnetoresistance effect element of the present
modification has a structure into which there are stacked a first
electrode 1'; a substrate layer 2' including a layer of Ta having a
thickness of 5 nm/a layer of Ru having a thickness of 2 nm; an
anti-ferromagnetic layer 3' formed from PtMn to a thickness of 15
nm or thereabouts; a magnetization fixed layer 4' formed from a
Co.sub.90Fe.sub.10 layer; a spacer layer 5' formed from Cu to a
thickness of 3 nm or thereabouts; a magnetization free layer 6'
formed from a layer of Co.sub.90Fe.sub.10; a first protective layer
7' formed from Cu to a thickness of about 1 nm; a second protective
layer 8' formed from Ru to a thickness of about 5 nm; and a second
electrode 9'. A function layer 10' is inserted into the
magnetization fixed layer 4'.
Even in the first modification, an advantage similar to that
achieved in the first embodiment is yielded.
Second Modification
FIG. 5 shows a magnetoresistance effect element as a second
modification of the first embodiment shown in FIG. 1, wherein the
position of the magnetization fixed layer and that of the
magnetization free layer are provided opposite, by way of the
spacer layer, the position of the magnetization fixed layer and
that of the magnetization free layer of the first embodiment shown
in FIG. 1.
As shown in FIG. 5, a magnetoresistance effect element of the
present modification has a structure where there are stacked a
first electrode 1''; a substrate layer 2'' formed from a layer of
Ta having a thickness of 5 nm and a layer of Ru having a thickness
of 2 nm; a magnetization free layer 6'' formed by affixing a
Co.sub.90Fe.sub.10 layer of 1.5 nm or thereabouts to the
magnetization layer such that a function layer 10-2'' is sandwiched
therebetween; a spacer layer 5'' formed from Cu to a thickness of 3
nm or thereabouts; a second magnetization fixed layer 4-3'' formed
by affixing a Co.sub.90Fe.sub.10 layer of 1.5 nm or thereabouts to
the magnetization layer such that a function layer 10-1'' is
sandwiched therebetween; a magnetization anti-parallel coupling
layer 4-2'' formed from Ru to a thickness of about 0.9 nm; a first
magnetization fixed layer 4-1'' formed from Co.sub.90Fe.sub.10 to a
thickness of about 3 to 4 nm; an anti-ferromagnetic layer 3''
formed from PtMn to a thickness of about 15 nm; a protective layer
8'' formed from Ru to a thickness of about 5 nm; and a second
electrode 9''. Even the second modification yields the same
advantage as that yielded by the first embodiment.
Second Embodiment
A method for manufacturing a magnetoresistance effect element of a
second embodiment of the present invention will now be described.
The second embodiment is different from the first embodiment in
that the material of the function layer is changed. Therefore,
clear differences between the first and second embodiments are
described, and explanations of similarities between them are
omitted.
After the first electrode 1 to the magnetization anti-parallel
coupling layer 4-2 have been formed through the processes described
in the first embodiment, Co.sub.90Fe.sub.10--which is a stacked
member and serves as a second magnetization fixed layer 4-3--is
stacked to 1.5 nm. During the course of formation of the second
magnetization fixed layer 4-3, the function layer 10-1 is formed
through the process such as that shown in FIGS. 2A-2E.
Specifically, the processes are as follows. First,
Fe.sub.50Co.sub.50 is grown to a thickness of 1 nm as a portion of
the second magnetization fixed layer 4-3 that is to become an
oxidized layer. Here, the term "a portion of the second
magnetization fixed layer 4-3" means a lower half of the second
magnetization fixed layer that is split into upper and lower
portions with the function layer 10-1 sandwiched therebetween, as
described in connection with the first embodiment.
The surface of Fe.sub.50Co.sub.50, which is a portion of the second
magnetization fixed layer 4-3, is subjected to natural oxidation,
ion beam oxidation (IAO: Ion Assisted Oxidation), or plasma
oxidation, thereby causing the function layer 10-1 to grow to a
thickness of about 1.5 nm to 3 nm on the surface of
Fe.sub.50Co.sub.50. Here, an ion beam is extremely weaker than that
employed in ordinary milling requirements, and a beam voltage is
set to 100V or less. An etch rate achieved when Co.sub.90Fe.sub.10
is exposed to an ion beam without oxygen under these requirements
is 3 angstrom/min. or thereabouts.
Process requirements for natural oxidization, IAO, and plasma
oxidization are as provided in Table 2 shown in FIG. 13.
In Table 2, reference symbol REF denotes, as a sample to be
referred, a process for a spin valve structure having no function
layer. Reference symbols C-1 to C-4 denote process conditions for a
conventional process of preparing a function layer. Reference
symbols D-1 to D-4 denote process conditions for a process of
preparing a function layer of the present invention.
A difference between the process conditions for the related-art
process of preparing a function layer and the process conditions
for the process of the present invention for preparing a function
layer lies in that AIT (After Ion Treatment) is performed when a
thin oxide film is formed by any one of natural oxidation, IAO, and
plasma oxidation, as in the case of the first embodiment. As a
result of AIT being performed, the function layer 10 can be formed,
while maintaining a uniform thickness, into a thin layer without
being formed into the shape of an island or having a plurality of
pin holes.
Subsequent to formation of the function layer 10 through the
above-described processes, processes from the process of forming
Co.sub.90Fe.sub.10--which is to become an upper half of the second
magnetization fixed layer 4-3--until the process of forming the
second electrode 9 are the same as those of the first embodiment,
and hence their explanations are omitted.
In the present embodiment, the function layer 10 is taken as an
oxide of FeCo. However, the function layer 10 is not limited to
this material as in the case of the first embodiment. The essential
requirement for the function layer 10 is to be an oxide, a nitride,
or a fluoride formed by oxidizing, nitriding, or fluorinating metal
or an alloy containing at least one member selected from the group
consisting of Fe, Co, Ni, Cu, Ti, V, Cr, Mn, Mg, Al, Si, Zr, Nb,
Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Ir, Pt, and Au.
Differences between the properties of the magnetoresistance effect
element manufactured under the manufacturing method of the second
embodiment of the present invention and the properties of the
magnetoresistance effect element manufactured under the
manufacturing method of the related-art manufacturing method will
now be described by reference to Table 2. From Table 2, even when
an FeCo alloy is used as a base material of the function layer 10,
the amount of increase in MR acquired in the sample group C
prepared according to the related-art process flow is not large.
However, the amount of increase in MR acquired in the sample group
D prepared according to the process flow of the present invention
is very large. This is also conceived that the uniform function
layer 10 is acquired in the group D.
When the magnetoresistance effect element is formed under the
method of the second embodiment and when RF plasma is effected
under the same conditions as those of the first embodiment; namely,
a beam voltage of 100V or less, the effect of the function layer
can be sufficiently utilized only when the RF power is set to 15 W
to 30 W, and a high MR ratio can be acquired.
A higher MR ratio can be realized, so long as a Co.sub.1-xFe.sub.x
alloy (50.ltoreq.x.ltoreq.100) including the composition of the
first embodiment and that of the second embodiment is used.
Third Embodiment
A method for manufacturing a magnetoresistance effect element of a
third embodiment of the present invention will now be described.
The third embodiment is different from the function layer of the
first embodiment in that the material of the function layer is
changed as in the case of the second embodiment. Therefore, clear
differences between the first and second embodiments are described,
and explanations of similarities between them are omitted.
After the first electrode 1 to the magnetization anti-parallel
coupling layer 4-2 have been formed through the processes described
in the first embodiment, Co.sub.90Fe.sub.10--which is a stacked
member and a second magnetization fixed layer 4-3--is stacked to
1.5 nm. During the course of formation of the second magnetization
fixed layer 4-3, the function layer 10-1 is formed through the
process such as that shown in FIGS. 2A-2E.
Specifically, the processes are as follows. First, Ti is grown to a
thickness of 1 nm as a portion of the second magnetization fixed
layer 4-3 that is to become an oxidized layer. Here, the term "a
portion of the second magnetization fixed layer 4-3" means a lower
half of the second magnetization fixed layer that is split into
upper and lower portions with the function layer 10-1 sandwiched
therebetween, as described in connection with the first
embodiment.
The surface of Ti, which is a portion of the second magnetization
fixed layer 4-3, is subjected to natural oxidation, ion beam
oxidation (IAO), or plasma oxidation, thereby causing the function
layer 10-1 to grow to a thickness of about 1.5 nm to 3 nm on the
surface of Ti. Here, an ion beam is extremely weaker than that
employed in ordinary milling requirements, and a beam voltage is
set to 100V or less. An etch rate achieved when Ti is exposed to an
ion beam without oxygen under these requirements is 0.1 to 3
angstrom/min. or thereabouts.
Process requirements for natural oxidization, IAO, and plasma
oxidization are as provided in Table 3 shown in FIG. 14.
In Table 3, reference symbol REF denotes, as a sample to be
referred to, a process for a spin valve structure having no
function layer. Reference symbols E-1 to E-4 denote process
conditions for a conventional process of preparing a function
layer. Reference symbols F-1 to F-4 denote process conditions for a
process of preparing a function layer of the present invention.
A difference between the process conditions for the related-art
process of preparing a function layer and the process conditions
for the process of the present invention for preparing a function
layer lies in that AIT (After Ion Treatment) is performed when a
thin oxide film is formed by any one of natural oxidation, IAO, and
plasma oxidation, as in the case of the first embodiment. As a
result of AIT being performed, the function layer 10 can be formed,
while maintaining a uniform thickness, into a thin layer without
being formed into the shape of an island or having a plurality of
pin holes.
Subsequent to formation of the function layer 10 through the
above-described processes, processes from the process of forming
Co.sub.90Fe.sub.10--which is to become an upper half of the second
magnetization fixed layer 4-3--until the process of forming the
second electrode 9 are the same as those of the first embodiment,
and hence their explanations are omitted.
In the present embodiment, the function layer 10 is taken as an
oxide of Ti. However, the function layer 10 is not limited to this
material. The essential requirement for the function layer 10 is to
be an oxide, a nitride, or a fluoride formed by oxidizing,
nitriding, or fluorinating metal or an alloy containing at least
one member selected from the group consisting of Fe, Co, Ni, Cu,
Ti, V, Cr, Mn, Mg, Al, Si, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W,
Re, Ir, Pt, and Au.
Differences between the properties of the magnetoresistance effect
element manufactured under the manufacturing method of the third
embodiment of the present invention and the properties of the
magnetoresistance effect element manufactured under the
manufacturing method of the related-art manufacturing method will
now be described by reference to Table 3. Even when Ti is used as a
base material of the function layer, the amount of increase in MR
in sample group E prepared according to the related-art process
flow is not large. However, the amount of increase in MR in the
sample group F prepared through the process flow of the present
invention is very large. It is also conceivable that a uniform
function layer is obtained in group F.
When the magnetoresistance effect element is formed under the
method of the third embodiment and when RF plasma is effected under
the same conditions as those of the first embodiment; namely, a
beam voltage of 100V or less, the effect of the function layer can
be sufficiently utilized only when the RF power is set to 15 W to
30 W, and a high MR ratio can be acquired.
Fourth Embodiment
A method for manufacturing a magnetoresistance effect element of a
fourth embodiment of the present invention will now be described.
The fourth embodiment is different from the function layer 10 of
the first embodiment in that the material of the function layer is
changed as in the case of the second embodiment. Therefore, clear
differences between the first embodiment and the fourth embodiment
are described, and explanations of similarities between them are
omitted.
After the first electrode 1 to the magnetization anti-parallel
coupling layer 4-2 have been formed through the processes described
in the first embodiment, Co.sub.90Fe.sub.10--which is a stacked
member and a second magnetization fixed layer 4-3--is stacked to
1.5 nm. During the course of formation of the second magnetization
fixed layer 4-3, the function layer 10-1 is formed through the
process such as that shown in FIGS. 2A-2E.
Specifically, the processes are as follows. First, Ti is grown to a
thickness of 1 nm as a portion of the second magnetization fixed
layer 4-3 that is to become an oxidized layer. Here, the term "a
portion of the second magnetization fixed layer 4-3" means a lower
half of the second magnetization fixed layer that is split into
upper and lower portions with the function layer 10-1 sandwiched
therebetween, as described in connection with the first
embodiment.
The surface of Zr, which is a portion of the second magnetization
fixed layer 4-3, is subjected to natural oxidation, ion beam
oxidation (IAO), or plasma oxidation, thereby causing the function
layer 10-1 to grow to a thickness of about 1.5 nm to 3 nm on the
surface of Zr. Here, an ion beam is extremely weaker than that
employed in ordinary milling requirements, and a beam voltage is
set to 100V or less. An etch rate achieved when Ti is exposed to an
ion beam without oxygen under these requirements is 0.1 to 3
angstrom/min. or thereabouts.
Process requirements for natural oxidization, IAO, and plasma
oxidization are as provided in Table 4 shown in FIG. 15.
In Table 4, reference symbol REF denotes, as a sample to be
referred to, a process for a spin valve structure having no
function layer. Reference symbols G-1 to G-4 denote process
conditions for a conventional process of preparing a function
layer. Reference symbols H-1 to H-4 denote process conditions for a
process of preparing a function layer of the present invention.
As in the case of the first embodiment, a difference between the
process conditions for the related-art process of preparing a
function layer and the process conditions for the process of the
present invention for preparing a function layer lies in that AIT
(After Ion Treatment) is performed when a thin oxide film is formed
by any one of natural oxidation, IAO, and plasma oxidation. As a
result of AIT being performed, the function layer 10 can be formed,
while maintaining a uniform thickness, into a thin layer without
being formed into the shape of an island or having a plurality of
pin holes.
Subsequent to formation of the function layer 10 through the
above-described processes, processes from the process of forming
Co.sub.90Fe.sub.10--which is to become an upper half of the second
magnetization fixed layer 4-3--until the process of forming the
second electrode 9 are the same as those of the first embodiment,
and hence their explanations are omitted.
In the present embodiment, the function layer 10 is taken as an
oxide of Zr. However, the function layer 10 is not limited to this
material. The essential requirement for the function layer 10 is to
be an oxide, a nitride, or a fluoride formed by oxidizing,
nitriding, or fluorinating metal or an alloy containing at least
one member selected from the group consisting of Fe, Co, Ni, Cu,
Ti, V, Cr, Mn, Mg, Al, Si, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W,
Re, Ir, Pt, and Au.
Differences between the properties of the magnetoresistance effect
element manufactured under the manufacturing method of the fourth
embodiment of the present invention and the properties of the
magnetoresistance effect element manufactured under the
manufacturing method of the related-art manufacturing method will
now be described by reference to Table 4. Even when Zr is used as a
base material of the function layer, the amount of increase in MR
in sample group G prepared according to the related-art process
flow is not large. However, the amount of increase in MR in the
sample group H prepared through the process flow of the present
invention is very large. It is also conceivable that a uniform
function layer is obtained in group H.
When the magnetoresistance effect element is formed under the
method of the fourth embodiment and when RF plasma is effected
under the same conditions as those of the first embodiment; namely,
a beam voltage of 100V or less, the effect of the function layer
can be sufficiently utilized only when the RF power is set to 15 W
to 30 W, and a high MR ratio can be acquired.
From the first through fourth embodiments, the thin-film formation
process shown in FIGS. 2A-2E is shown to be useful as the method
for manufacturing the function layers 10 of various materials. In
addition, even when Ti, Cr, Zr, Hf, V, Al, Mg, or Cu is used for
the function layer 10, a uniform function layer is understood to be
acquired by causing the material to pass through the thin-film
formation process in the same manner, and a high MR ratio is
understood to be obtained.
Fifth Embodiment
A method for manufacturing a magnetoresistance effect element of a
fifth embodiment of the present invention will now be described.
The fifth embodiment is different from the first through fourth
embodiments in that the function layer 10 is formed as a stacked
member. In other respects, the fifth embodiment is essentially
identical with the first through fourth embodiments, and hence
clear differences between the fifth embodiment and the first
through fourth embodiments are described, and explanations of
similarities among them are omitted.
After the first electrode 1 to the magnetization anti-parallel
coupling layer 4-2 have been formed through the processes described
in the first embodiment, Co.sub.90Fe.sub.10--which is a stacked
member and a second magnetization fixed layer 4-3--is stacked to
1.5 nm. During the course of formation of the second magnetization
fixed layer 4-3, the function layer 10-1 is formed through the
process such as that shown in FIGS. 2A-2E.
Specifically, the processes are as follows. First, Fe is grown to a
thickness of 0.15 nm as a portion of the second magnetization fixed
layer 4-3 that is to become an oxidized layer; and, subsequently,
Zr is grown to a thickness of 0.15 nm. Here, the term "a portion of
the second magnetization fixed layer 4-3" means a lower half of the
second magnetization fixed layer that is split into upper and lower
portions with the function layer 10-1 sandwiched therebetween, as
described in connection with the first embodiment.
Fe and Zr, which are portions of the second magnetization fixed
layer 4-3, are subjected to natural oxidation, ion beam oxidation
(IAO), or plasma oxidation, thereby causing the function layer 10-1
to grow to a thickness of about 1.5 nm to 3 nm on the surface of Fe
and Zr. Here, an ion beam is extremely weaker than that employed in
ordinary milling requirements, and a beam voltage is set to 100V or
less. An etch rate achieved when a multilayer body consisting of Fe
and Zr is exposed to an ion beam without oxygen under these
requirements is 0.1 to 3 angstrom/min. or thereabouts.
Process requirements for natural oxidization, IAO, and plasma
oxidization are as provided in Table 5 shown in FIG. 16.
In Table 5, reference symbol REF denotes, as a sample to be
referred to, a process for a spin valve structure having no
function layer. Reference symbols I-1 to I-4 denote process
conditions for a related-art process of preparing a function layer.
Reference symbols J-1 to J-4 denote process conditions for a
process of preparing a function layer of the present invention.
As in the case of the first embodiment, a difference between the
process conditions for the related-art process of preparing a
function layer and the process conditions for the process of the
present invention for preparing a function layer lies in that AIT
(After Ion Treatment) is performed when a thin oxide film is formed
by any one of natural oxidation, IAO, and plasma oxidation. As a
result of AIT being performed, the function layer 10 can be formed,
while maintaining a uniform thickness, into a thin layer without
being formed into the shape of an island or having a plurality of
pin holes.
Subsequent to formation of the function layer 10 through the
above-described processes, processes from the process of forming
Co.sub.90Fe.sub.10--which is to become an upper half of the second
magnetization fixed layer 4-3--until the process of forming the
second electrode 9 are the same as those of the first embodiment,
and hence their explanations are omitted.
In the present embodiment, the function layer 10 is taken as an
oxide of Fe--Zr. However, the function layer 10 is not limited to
this material. The essential requirement for the function layer 10
is to be an oxide, a nitride, or a fluoride formed by oxidizing,
nitriding, or fluorinating metal or an alloy containing at least
one member selected from the group consisting of Fe, Co, Ni, Cu,
Ti, V, Cr, Mn, Mg, Al, Si, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W,
Re, Ir, Pt, and Au.
Differences between the properties of the magnetoresistance effect
element manufactured under the manufacturing method of the fifth
embodiment of the present invention and the properties of the
magnetoresistance effect element manufactured under the
manufacturing method of the related-art manufacturing method will
now be described by reference to Table 5. Even when Zr is used as a
base material of the function layer, the amount of increase in MR
in sample group I prepared according to the related-art process
flow is not large. However, the amount of increase in MR in the
sample group J prepared through the process flow of the present
invention is very large. It is also conceivable that a uniform
function layer is obtained in group J. Further, since the function
layer 10 is a multilayer body, there is achieved an MR which is
greater than that achieved in the second and third embodiments
where the function layer 10 is formed as a single layer. The reason
for this is considered to be that modulation of the electron
structure of the function layer 10 induces somewhat spin
polarization effect in conduction electrons, thereby yielding a
great spin filtering effect.
Even in the present embodiment, in a case where AIT is used for the
thin film formation process, when RF plasma is effected under the
same conditions as those of the first embodiment; namely, a beam
voltage of 100V or less, the effect of the function layer can be
sufficiently utilized only when the RF power is set to 15 W to 30
W, and a high MR ratio can be acquired.
The combination of stacked members of the present embodiment is not
limited to the example mentioned above. A stacked member can yield
the same advantage as that yielded in the present embodiment, so
long as the stacked member is formed from two types of materials
selected from Ti, Cr, Zr, Hf, V, Al, Mg, and Cu.
Sixth Embodiment
In the first through fifth embodiments, the function layer is
assumed to be included in either the magnetization fixed layer or
the magnetization free layer or both. The sixth embodiment examines
the degree of difference between the MR ratio achieved when the
function layer is included in either the magnetization fixed layer
or the magnetization free layer and the MR ratio achieved when the
function layer is included in both the magnetization fixed layer
and the magnetization free layer.
A characteristic required by the magnetoresistance effect element
is a magnetic characteristic as well as the rate of a change in
resistance. Particularly, when an increase has arisen in the
coercive force Hc and the magnetostriction .lamda. of the
magnetization free layer, the magnetic characteristic becomes the
source of noise, or a response to an external magnetic field which
is a signal becomes deteriorated. When the element is used as a
magnetic head, a signal-to-noise ratio is lost. Accordingly, Hc and
.lamda. of the magnetization free layer must be minimized. In
general, when a ferromagnetic substance is mixed with oxygen, Hc
and .lamda. are known to increase. Since the function layer of the
present invention is chiefly formed from an oxygen layer, there is
a possibility of Hc and .lamda. increasing when the function layer
is inserted into the magnetization free layer, thereby
deteriorating the signal-to-noise ratio. However, in connection
with a loss induced by the deterioration of the magnetic
characteristic and an improvement in MR, when an advantage of
improvement in MR is great, no problem arises even when the
function layer is inserted into the magnetization free layer. In
addition, there is an advantage of a configuration where the
function layer is inserted solely into the magnetization free layer
being readily realized in reality.
As an example, on the premise that the function layer is in the
magnetization fixed layer in the first embodiment, separate
consideration is given to a case where the function layer is in the
magnetization free layer and a case where the function layer is not
in the magnetization free layer. Table 6, shown in FIG. 17, shows
results of measurement of the MR ratios. Incidentally, Table 6 also
shows a configuration (Co.sub.90Fe.sub.10 1 nm/Ni.sub.80Fe.sub.20
3.5 nm) where the magnetic characteristics of the free layer become
better.
According to Table 6, as in the case of the results of the first
through sixth embodiments, the samples (B-1 to B-4, L-1 to L-4, O-1
to O-4) that have undergone AIT when a thin oxide film is formed in
the magnetization fixed layer by any one of natural oxidation, IAO,
and plasma oxidation are understood to be higher in MR ratio than
the samples (A-1 to A-4, K-1 to K-4, M-1 to M-4) having not
undergone AIT. As is evident from a comparison between A-2 and K-2,
and between M-2, B-1 and L-1, O-1, the effect of an improvement in
MR ratio considerably decreases when the function layer is inserted
solely into the magnetization fixed layer.
By a comparison among the sample groups B-1 to B-4, L-1 to L-4, and
O-1 to O-4 and a comparison among the sample groups A-1 to A-4, K-1
to K-4, and M-1 to M-4, the samples into which the function layer
is inserted into the magnetization free layer can exhibit a greater
spin filtering effect. Accordingly, a greater MR ratio can be
acquired.
Seventh Embodiment
In the magnetoresistance effect elements described in connection
with the first through sixth embodiments, the spacer layer 5 is
formed from Cu. In the seventh embodiment, a study has been
conducted as to whether or not the advantage of the present
invention is yielded by a magnetoresistance effect element having a
resistance adjustment layer as the spacer layer 5. The resistance
adjustment layer employed herein is an NOL (Nano Oxide Layer)
formed from an Al--O having a metal path made of Cu. The Cu metal
path passes through the Al--O which is an insulating portion, and
connects the magnetization fixed layer to the magnetization free
layer in an ohmic manner.
A conceptual rendering of the magnetoresistance effect element of
the seventh embodiment is shown in FIG. 9. The structure of the
seventh embodiment exhibits a so-called CCP (Current-Confined Path)
effect, wherein an electric current is confined in the vicinity of
the magnetization fixed layer 104, the spacer layer 105, and the
free layer 106, which are dependent on a spin. Hence, an MR ratio
is increased. As an example, Table 7, shown in FIG. 18, shows a
result of measurement of MR ratio in the magnetoresistance effect
element in which the function layers described in connection with
the first through fifth embodiments and the spacer layer of the
Al--NOL structure having a Cu metal path are combined together.
According to Table 7, the MR ratios of the magnetoresistance effect
elements (P-1 to P-4, and Q-1 to Q-4), each having a spacer layer
105 of an Al--NOL structure having a Cu metal path, are about six
to seven times as large as the MR ratios (achieved by the elements
A-1 to A-4, and B-1 to B-4), each of which has the structure
described in connection with the first through fifth
embodiments.
As above, the magnetoresistance effect element having the spacer
layer 105 of Al--NOL structure with the Cu metal path can also
maintain the advantage of the present invention; namely, an
improvement in the MR ratio realized by the function layer formed
by subjecting the magnetization fixed layer and the magnetization
free layer to oxidation and AIT treatment.
Eighth Embodiment
In the first through sixth embodiment, the position of the function
layer is assumed to be located in the vicinity of an
essentially-intermediate position between the magnetization fixed
layer and the magnetization free layer. However, the spin filtering
effect in the magnetization fixed layer or the magnetization free
layer ought to be achieved equally everywhere.
However, in the case of the magnetoresistance effect element having
a resistance adjustment layer in the spacer as shown in the seventh
embodiment, the current confined effect becomes greater as the
distance to the spacer becomes smaller. Accordingly, an increase in
a spin-dependent scattering phenomenon achieved in the vicinity of
the interface between the magnetization fixed layer and the
magnetization free layer is greatly significant. Therefore, the
positional dependence of the function layer on the magnetization
fixed layer and the magnetization free layer will now be
examined.
As a comparative example, the MR ratio of the magnetoresistance
effect element where the function layer is located at the position
(a distance 1.5 nm from the interface) between the magnetization
fixed layer and the magnetization free layer in the seventh
embodiment is compared with the MR ratio of the magnetoresistance
effect element having a configuration where the function layer of
the present embodiment is located at a position (0.7 nm from the
interface). A result of comparison is provided in Table 8 shown in
FIG. 19.
As is also evident from Table 8, the MR ratios achieved in the
sample R group and those acquired in the S group can be ascertained
to be greater than the MR ratios achieved in the sample group P and
the sample group Q. Further, as the function layer is close to the
spacer player, the spin filtering effect is understood to appear
remarkably. As in the case of the previously-described embodiment,
when the sample R group and the sample S group are compared with
each other, the MR ratio is understood to become greater in the
function layer formed through the thin-film formation process such
as that shown in FIGS. 2A-2E.
Ninth Embodiment
In all of the first through eighth embodiments, the function layer
is prepared in the magnetization fixed layer or the magnetization
free layer, and the function layer has been verified to play a
great role in improvement of the MR ratio. However, spin-dependent
scattering responsible for fluctuations in an MR ratio does not
appear solely in the magnetization fixed layer or the magnetization
free layer. Conduction electrons are subjected to spin-dependent
scattering even in the interface between the spacer layer and the
magnetization fixed layer or the interface between the
magnetization free layer and the spacer layer.
Accordingly, in the ninth embodiment, there is conducted a study on
the position of the function layer in the magnetization fixed layer
or the magnetization free layer, wherein the function layer
increases spin-dependent scattering at the interface between the
spacer layer and the magnetization fixed layer or the magnetization
free layer.
FIG. 8 shows the magnetoresistance effect element of the ninth
embodiment. In FIG. 8, the magnetoresistance effect element of the
present embodiment has a structure where there are stacked a first
electrode 201; a substrate layer 202 including a Ta layer of 5 nm
and an Ru layer of 2 nm; an anti-ferromagnetic layer 203 formed
from PtMn to a thickness of about 15 nm; a magnetization fixed
layer 204 including a first magnetization fixed layer 204-1 formed
from Co.sub.90Fe.sub.10 to a thickness of 3 to 4 nm or thereabouts,
a magnetization anti-parallel coupling layer 204-2 formed from Ru
to a thickness of about 0.9 nm or thereabouts, and a second
magnetization fixed layer 204-3 formed from Co.sub.90Fe.sub.10
layer; a spacer layer 205 formed from Cu to a thickness of about 3
nm; a magnetization free layer 206 formed from a Co.sub.90Fe.sub.10
layer; a first protective layer 207 formed from Cu to a thickness
of about 1 nm; a second protective layer 208 formed from Ru to a
thickness of about 5 nm; and a second electrode 209.
A function layer 210-1 exists along an interface between the second
magnetization fixed layer 204-3 and the spacer layer 205, and the
function layer 210-2 exists along an interface between the
magnetization free layer 206 and the spacer layer 205. The total
thickness of the second magnetization fixed layer 204-3 and the
function layer 210-1 is about 3 nm, and the total thickness of the
magnetization free layer 206 and the function layer 210-2 is about
3 nm.
Table 9, shown in FIG. 20, shows a comparison between the magnitude
of the MR ratio acquired in the magnetoresistance effect element,
where the function layer is provided in the magnetization fixed
layer, and the MR ratio acquired in the magnetoresistance effect
element, where the function layer exists along the interface
between the magnetization fixed layer and the spacer layer. The
oxide layer of Fe used in the first embodiment is applied to the
function layer. Those oxidation conditions, AIT conditions, and the
like, which are used for the sample groups A-1 to A-4 and B-1 to
B-4 of the first embodiment, are used in an unmodified form.
According to Table 9, even when the function layer 210-1 is
inserted along the interface between the second magnetization fixed
layer 204-3 and the spacer layer 205, or the function layer 210-2
is inserted along the interface between the magnetization free
layer 206 and the spacer layer 205, a spin filtering effect similar
to that yielded in the first through eighth embodiments is yielded.
Moreover, as in the case of the first through eighth embodiments,
the MR ratios of the samples (U-1, U-2, U-3, and U-4) whose
function layers are formed through the thin film formation process
shown in FIGS. 2A-2E are understood to have become greater than the
MR ratios of the samples (T-1, T-2, T-3, and T-4) of the
magnetoresistance effect element having the functions which are
formed through a process not including the thin film formation
process such as that shown in FIGS. 2A-2E. The reason for this is
that a function layer having a uniform thickness can be grown in
the process shown in FIGS. 2A-2E, as has been described in
connection with the first embodiment and the like.
As mentioned above, in the ninth embodiment, the function layer
210-1 is inserted along the interface between the second
magnetization fixed layer 204-3 and the spacer layer 205, or the
function layer 210-2 is inserted along the interface between the
magnetization free layer 206 and the spacer layer 205. However, the
function layer may be inserted between the two interfaces. In that
case, a synergistic effect of the spin-filtering effect yielded by
the second magnetization fixed layer and the spin-filtering effect
yielded by the magnetization free layer is exhibited. Moreover, the
magnetoresistance effect element having a higher MR ratio can be
manufactured.
Tenth Embodiment
Although all of the above embodiments relate to the
magnetoresistance effect elements of the GMR structure, the present
invention is not limited to the GMR structure but may also be
applied to a TMR structure. In the present embodiment, there is
shown a magnetoresistance effect element in which a function layer
is formed from a TMR structure. In the TMR structure, the function
layer of the GMR structure corresponds to a barrier layer. The
magnetoresistance effect element of the TMR structure currently
encounters the problem of a reduction in RA of a reproduction head
of a hard disk drive. In order to achieve a lower RA, the thickness
of the barrier layer must be reduced. Incidentally, when the
thickness of the barrier layer is reduced, there arises a problem
of formation of pin holes in the barrier layer and a significant
reduction in MR.
In FIG. 10, the magnetoresistance effect element of the present
embodiment has a structure where there are stacked a first
electrode 201; a substrate layer 202 including a Ta layer of 5 nm
and an Ru layer of 2 nm; an anti-ferromagnetic layer 203 formed
from PtMn to a thickness of 15 nm; a magnetization fixed layer 204
including a first magnetization fixed layer 204-1 formed from
Co90Fe10 to a thickness of 3 to 4 nm or thereabouts, a
magnetization anti-parallel coupling layer 204-2 formed from Ru to
a thickness of about 0.9 nm or thereabouts, and a second
magnetization fixed layer 204-3 formed from Co.sub.90Fe.sub.10
layer to a thickness of 2 nm or thereabouts; a barrier layer 211
formed from AlO; a magnetization free layer 206 having a two-layer
structure having a Co.sub.75Fe.sub.25 layer of about 2 nm and an
Ni80Fe20 layer of about 3.5 nm; a first protective layer 207 formed
from Cu to a thickness of about 1 nm; a second protective layer 8
formed from Ru to a thickness of about 5 nm; and a second electrode
9.
Table 10, shown in FIG. 21, shows processes for forming the barrier
layer 211.
Table 10 shows that all of the samples W-1, W-2, W-3, and W-4,
where the barrier layers are formed through the processes shown in
FIGS. 2A-2E, exhibit MR ratios which are greater than those
exhibited by the samples V-1, V-2, V-3, and V-4 formed from thick
AlO from the beginning. The reason for this is that the number of
pin holes is decreased and that a uniform barrier layer is
created.
In the tenth embodiment, the barrier layer is taken as an oxide of
Al. However, the barrier layer is not limited to this material. The
essential requirement for the barrier layer is to be an oxide, a
nitride, or a fluoride formed by oxidizing, nitriding, or
fluorinating metal or an alloy containing at least one selected
from the group comprising Fe, Co, Ni, Cu, Ti, V, Cr, Mn, Mg, Al,
Si, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Ir, Pt, and Au. Even
in this case, a barrier layer can be made uniform through the
thin-film formation process.
In the tenth embodiment, the barrier layer is subjected to the
processes of the present invention. As in the case of the first
through ninth embodiments, the present invention is also naturally
applied as a process for forming a function layer to be inserted
into the magnetization fixed layer or the magnetization free
layer.
The present invention is not limited to the embodiments set forth.
In a practical stage, constituent elements can be embodied while
being modified without departing from the gist of the invention.
Various inventions can be created by an appropriate combination of
the plurality of constituent elements described in the embodiments.
For instance, some constituent elements may be deleted from all of
the constituent elements described in the embodiments. Moreover,
the constituent elements described in the different embodiments may
also be combined as appropriate.
According to the method of the present invention for manufacturing
a magnetoresistance effect element, there can be provided a
magnetoresistance effect element which exhibits a large amount of
change in magnetoresistance, high reliability, and high magnetic
stability. Consequently, highly-sensitive magnetic detection is
stably achieved. There can be provided a magnetic head which
exhibits a high signal-to-noise ratio even at high recording
density and a high output; a magnetic reproducing apparatus
equipped with the head; and highly-integrated magnetic memory.
* * * * *